In industrial control systems, it is often desirable to move objects from one location to another for accomplishing various tasks. For example, rolling conveyors are often used to move objects from one location to another for interacting with different machines of an industrial control process, such as a first machine at a first location for placing a box, a second machine at a second location for filling the box, and a third machine at a third location for closing the box.
More recently, a track system has been developed in which multiple “carts” can be independently driven along a “track” for accomplishing the various tasks of the industrial control process. By providing independently controllable carts, the timing of each task can be more precisely controlled than traditional systems such as rolling conveyors.
In such track systems having moving carts, it is often desirable to know the position of each cart at all times to ensure that the industrial control process is executing correctly. To accomplish this, each cart can be configured with a magnetic encoder scale, and the track can be configured with arrays of magnetic sensors with an air gap between the magnetic encoder scale and the magnetic sensors. In operation, when a magnetic encoder scale on a moving cart is near a group of magnetic sensors on the track, the magnetic sensors can determine the absolute position of the cart by measuring the varying magnetic field strength or varying magnetic field angle from the magnetic encoder scale on the cart. Conversely, when the cart is away from the group of magnetic sensors on the track, the magnetic sensors no longer sense the position magnet of the cart and, in turn, no longer generate output signals having measurable amplitudes. Accordingly, the magnetic sensors can be used to determine absolute positions of carts on the track. This is sometimes referred to as an encoder system.
However, encoder systems using magnetic sensors typically require calibration in the system in order to be effective. In addition, such magnetic sensors are typically sensitive to temperature variations that change sensor sensitivity and therefore measurement accuracy. Consequently, a need exists to provide a system for monitoring positions of carts on a track that eliminates one or more of the foregoing disadvantages.